Removing and replacing aircraft batteries is an important part of regular maintenance of modern business jets, and these batteries are heavy and often located in areas of the aircraft that are difficult to easily access, sometimes requiring aircraft mechanics to attempt to hold the 90 lb. batteries at antis length above their heads, risking injury to themselves, and damage to the battery and/or the aircraft.
Servicing the two main batteries in the Bombardier Lear 60 is illustrative of the problem. Behind the access door at the tail of the aircraft is the auxiliary power unit (APU), which must first be removed to access the two batteries, which are located above and behind the APU. The battery closest to the access door is provided with a stirrup-operated cable lift, consisting of a platform on vertical rails that is connected to a cable and pulley system by which the aircraft mechanic can lower the battery into the space formerly occupied by the APU by putting one foot in a loop of cable and slowly raising his leg. After completing that awkward operation, there still remains a second battery located on a fixed shelf behind the first, which is now accessible thanks to the removal of the APU and the first battery creating a path to the access door. Once the first battery has been removed from the cable lift platform, and the cable lift platform itself removed from its vertical rails, the aircraft mechanic is then faced with reaching up to the battery shelf in this cramped space, and removing the second battery without any built-in support to aid in the operation.
Not only must these batteries be removed on a regular schedule as part of routine maintenance of the aircraft, either at six or twelve month intervals depending upon the battery type, but because of their location at the access door of the Lear 60, the APU and the batteries must be removed first before servicing almost any other systems in the tail section of the aircraft. An external lift suitable for supporting and removing aircraft batteries would therefore be desirable.
The need for lifts for servicing aircraft batteries has been recognized for a long time. U.S. Pat. No. 2,465,796 to Freeman (1949) shows a lift with a load support that could be raised and lowered on a continuous loop of chain, and which featured a tilting boom to bring the battery close to the aircraft fuselage. Given the scale of the Freeman lift relative to the battery depicted, and advances in battery technology that have occurred since that time to reduce the weight and size of batteries, the Freeman lift must have been rather large. The Freeman lift's use of a tilting boom to bring the battery into proximity with the location where it is to be installed in the aircraft, especially when there appears to be no provision for controlling the weight at the end of the boom other than the operator's strength in holding the lever, appears to risk damage to the aircraft, or, given a sufficient battery weight and position of the maneuverable front wheel, toppling of the lift itself on its tripod-like wheeled carriage. Despite its apparent size, the Freeman lift appears to have been operable by one person.
A major vendor of ground support equipment, Tronair, Inc., 1740 Eber Rd., Holland, Ohio 43528, offers a hydraulically operated device they term a “universal lift,” for which various adapters are available, including load platforms for supporting aircraft batteries. However, the Tronair lift, which resembles an engine hoist, is bulky, weighing over 260 pounds, and requires a substantial amount of hangar space to store. Due to the 82″ overall length of the Tronair lift, and the location of the handles for guiding the lift at the opposite end of the horizontal support arm from the load platform, the operator guiding the lift cannot readily see the position of the load platform relative to the cramped space inside the access door of an aircraft like the Lear 60. The jack handle for pressurizing the hydraulic cylinder which raises the horizontal support arm of the Tronair lift is located at the base of the lift opposite from the load platform, also making it difficult for the operator to readily judge the position of the load platform as vertical adjustments are made. The Tronair lift therefore optimally requires two people to position it, one to guide the lift and operate the hydraulic cylinder, and another to act as “spotter,” providing the operator with instructions concerning the position of the load platform.
The Tronair lift is hydraulically operated, and so vertical adjustments of the horizontal support arm are accomplished by pumping the jack handle of the hydraulic cylinder to raise the arm, or opening the release valve of the hydraulic cylinder to lower the arm. Coarse adjustments of the vertical position of the load platform are therefore slow, and precise vertical adjustments must be performed even more carefully, because if the desired height is exceeded, depressurizing the hydraulic cylinder by means of the release valve to the precise degree needed to correct the elevation is difficult.
A further disadvantage of Tronair's prior art “universal lift” is the size of the load platform itself, which is 12″ square. In servicing the batteries of the Lear 60, for example, the Tronair “universal lift” load platform is too wide to fit between the rails of the stirrup-operated cable lift, and thus the load platform cannot be raised to the level of the shelf holding the second battery.
It is therefore an object of the present invention to provide a compact, easily maneuverable lift suitable for servicing aircraft, and which is particularly applicable to servicing heavy parts such as batteries. It is a further object of the present invention to provide at least one of the following: a lift that can be readily positioned and operated by one person, a lift that is quickly and accurately adjustable to the desired height, a lift having a load platform that can fit into tight spaces, and a lift that is simple to manufacture.